The General Packet Radio Service (GPRS) is an enhancement to the so-called Global System for Mobile Communication (GSM) to provide packet data services to GSM subscribers. GPRS aims at making efficient use of GSM radio resources for bursty packet data transfer. This is in contrast to conventional circuit switched data services currently available in GSM. Presently, the GPRS core network (CN) is based on GPRS Tunneling Protocol (GTP) using the well known User Datagram Protocol/Internet Protocol (UDP/IP) or Transmission Control Protocol/Internet Protocol (TCP/IP) network which supports only best-effort service. A more detailed description of GTP is found in ETSI Standard GSM 09.60, Release 1998, entitled “General Packet Radio Service (GPRS): GPRS Tunneling Protocol (GTP) Across The Gn And Gp Interface,” the teachings of which are incorporated herein by this reference.
A portion of a typical GPRS system 100 is illustrated in FIG. 1. The core network 102, 104 (which may comprise, as shown, multiple IP networks coupled together via a gateway 103 ) is the primary transport mechanism in the GPRS system 100. GPRS introduces two new GPRS Support Nodes (GSNs), namely one or more Serving GPRS Support Nodes (SGSN) 112–116 and one or more Gateway GPRS Support Nodes (GGSN) 108–110, into the GSM architecture in order to support packet data services. Each SGSN 112–116 maintains the mobility context for mobile stations (MS) 122 (only one shown) and also performs authentication procedures. Any given SGSN 112 is coupled to a Base Station Subsystem (BSS) 118 over a frame relay network on one side and to various GGSNs 108–110 over the core network 102, 104 on the other side. Each BSS 118 is in turn coupled to a Mobile Switching Center (MSC) 120 that allows communication with the rest of the GSM circuit-switched architecture. Each BSS 118 supports wireless communications with each MS 122 within its coverage area. Each GGSN 108–110 acts as a gateway to public data networks 106, such as the Internet. Note that the core network 102, 104 typically comprises a plurality of IP-based intermediate nodes, e.g., routers, which support the communication paths within the core network 102, 104.
As currently specified, data packets are transported between a SGSN and GGSN using IP tunnels, as known in the art. For example, a given GGSN 108 encapsulates an IP packet destined to the MS 122 into another IP packet after attaching a GTP header to it. The outer (or encapsulating) IP header has the serving SGSN's 112 (i.e., the one that maintains the current mobility context for the MS) IP address as the destination address. The encapsulated packet is then forwarded through the CN 102 using hop-by-hop forwarding. At the serving SGSN 112, the outer IP header is stripped. The serving SGSN 112 uses the GTP header to forward the packet to the MS 122 via the appropriate BSS 118 using link layer procedures, i.e., over a radio access bearer. The GPRS Tunneling Protocol implemented at each of the SGSN 112–116 and GGSN 108–110 is responsible for performing these tasks of encapsulation and mapping onto an appropriate radio access bearer. Packet Data Protocol (PDP) is used to perform signaling tasks of GTP. A more detailed depiction of the various communication protocols used in current GPRS systems is illustrated in FIG. 2. In particular, a protocol “stack” is shown at each device inclusively between the MS and GGSN. Based on the Open System Interconnection (OSI) model, each layer of the respective protocol stacks represents an additional layer of functionality. Physical communication, e.g., modulation protocols and the like, occurs at the lowest layer, whereas the most functionality occurs at the top. Each of the various layers illustrated in FIG. 2 are well known in the art and are discussed in greater detail in ETSI Standard GSM 03.60, Release 1997, entitled “General Packet Radio Services (GPRS): Service Description,” the teachings of which are incorporated herein by this reference. The solid lines between layers indicate peering relationship (i.e., residing at the same protocol layer) between protocol layers. Note, for example, that GTP is terminated in the SGSN and GGSN. Also note that there are typically a number of intermediate nodes between the GGSN and SGSN, although only a single intermediate node is illustrated in FIG. 2 for clarity.
In contrast to the single (best effort) level of service provided by the GPRS CN, it is anticipated that varying levels of service will become a requirement. For example, the so-called Universal Mobile Telecommunications System (UMTS), based on the GPRS network architecture described above, defines four different quality of service (QoS) or traffic classes as defined in 3 GPP Technical Specification 23.107, Release 1999, entitled “3rd Generation Partnership Project (3 GPP): Technical Specification Group Services and System Aspects: QoS Concepts and Architectures,” the teachings of which are incorporated herein by this reference. These classes are the conversational class, the streaming class, the interactive class and the background class. The main distinguishing factor between these classes is the delay sensitivity of each type of traffic. The conversational class is meant for very delay sensitive traffic, whereas the background class is the most delay insensitive traffic class. The conversational and streaming classes are mainly intended to be used to carry real-time traffic flows. Conversational real-time services, like video telephony, are the most delay sensitive applications and those data streams should be carried in the conversational class. The interactive and background classes are mainly meant to be used by traditional Internet applications like World Wide Web (WWW), Email, Telnet, File Transfer Protocol (FTP) and News. The main difference between the interactive and background classes is that the interactive class is mainly used by interactive applications, e.g. interactive Email or interactive Web browsing, whereas the background class is meant for background traffic, e.g. background download of Emails or background file downloading. Separating interactive and background applications ensures responsiveness of the interactive applications. Traffic in the interactive class has higher priority in scheduling than traffic in the background class, so background applications use transmission resources only when interactive applications do not need them. Compared to conversational and streaming classes, both provide better error rate by means of channel coding and retransmission available due to the looser delay requirements. As more and more communication services (besides data) are being offered over IP, it becomes critical for the GPRS CN to be able to support UMTS QoS classes.
Other researchers have recognized the need for IP QoS provisioning in the GPRS CN. In particular, in “Quality of Service Framework in GPRS and Evolution towards UMTS,” M. Puuskari, 3 rd European Personal Mobile Communication Conference, March 1999; “Supporting IP QoS in the General Packet Radio Service,” Priggouris et al., IEEE Network, pp. 8–17, September/October 2000; and “An Integrated QoS Architecture for GSM Networks,” Mikkonen et al., International Conference on Universal Personal Communication (ICUPC), vol. 1, pp. 403–407, October 1998, the authors have discussed the possibility of using Integrated Services (IntServ) QoS mechanism in the CN. The proposal in the Priggouris et al. paper uses RSVP messaging between SGSN and GGSN to establish QoS enabled GTP tunnels across the CN. In the Mikkonen et al. paper, the authors propose the use of GSM circuit switched services for the guaranteed service class of IntServ, and the GPRS packet switched services for the controlled load class of IntServ. However, the IntServ QoS mechanism is notably complex and has poor scalability in large networks. Further, when an MS changes its serving SGSN due to mobility, the QoS-enabled GTP tunnels have to be re-established between the GGSN and the new SGSN. In the IntServ approach stated above, RSVP messaging and resource reservation has to be reinitiated between the GGSN and the new SGSN. This increases the complexity of IntServ approach and adds more latency to the handover procedure. The possibility of using Differentiated Services (DiffServ) approach rather than IntServ approach is also briefly discussed in the above references.
Therefore, it would be advantageous to provide a technique that supports various QoS classes across the GPRS core network in a scalable and efficient way.